1. Field of the Invention
For the purpose of storage under an elevated or reduced pressure there has been known no large container, but only small containers for food storage commonly known as canned food. Containers with openable top lid are generally known to be unable to provide sufficient pressure resistance, so that containers with sealed small apertures for particular purposes requiring pressure resistance. Such containers generally have very small apertures and are therefore extremely inconvenient for filling and taking out of the content unless it is liquid or powder. Also in such containers the seal has to be destructed for opening the container.
In the field of food industry there are not yet used satisfactory large containers, although the demand for such large containers was pointed out years ago in relation to the change in the food distribution channels and to the introduction of larger transportation vehicles.
2. Description of the Prior Art
Among recent food distribution containers there are known so-called retort food containers of a capacity in the order of 10 liters, which are used both for the food processing and for the food transportation, and which are provided with corrugated shapes on the bottom in order to cope with the deformation by a reduced pressure resulting from vapor condensation induced by a fact that the container is sealed immediately after the content is processed. Such containers, however, cannot be used repeatedly since the lid has to be forced open. There are also known improved containers with fitted lids, but such containers are still associated with a difficulty in filling and taking out of the content. Moreover such retort food containers do not maintain a constant reduced pressure therein and the food is recommended for consumption within a determined period after processing, so that such containers do not have a function of periodic check of the internal reduced pressure.
In this manner a container for prolonged storage which is provided with a valve for pressure release and pressure inspection and is repetitively usable, as aimed at by the present invention, has never been known in the prior art.